Analysis and improvement of circuit design defects

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Analysis and improvement of the circuit design defects of S5012 tower crane

our company purchased a S5012 (QTZ63) tower crane from a construction machinery group company in October 2001. This tower crane is designed and manufactured by the group company itself. Since the date of installation and commissioning, the machine has always had the fault of frequent tripping of the automatic switch of the main power supply and the automatic switch of the lifting motor, with an average of more than 20 trips per day and a maximum of more than 40 trips. From October 18, 2001 to June 10, 2002, it took 199 working days to replace 11 AC contactors and 5 automatic switches of the hoisting system

the existence of this problem not only affects construction production, but also poses a serious threat to safety production. Because after the automatic switch of the main power supply tripped, the whole machine was powered off, the tower crane was out of control, the jib rotated with the wind, and the hook could not be lifted, luffed, or braked, and the lifted object nearly hit the construction personnel, bulk cement tanks, and other temporary facilities several times. For the sake of safety, we can only send an operator to start the machine on the tower crane, and an electrician is under the tower crane ready to send power at any time. (it's not safe for the operator, so we should solve the problem first, and then send someone up. -- editor)

the group company has sent two electricians to the site for repair four times. After each repair, the tripping frequency decreased, but it returned to its original state after two or three days. The repairmen of the group company first talked about the operation problems of the operators, and then thought that the capacity of electrical components was small. After these possibilities were ruled out, the repairman said that there was nothing he could do. Because other users also had this problem, the problem had to be handled by the group company. However, the group company has not come up with a treatment plan

in this case, we can only rely on our own strength to study and solve the problem, and then press the sample clamping key to start moving the clamping length, that is, repeat the steps ② - ⑤ until the set number of times is completed. At this time, the number of times is displayed as zero to solve this problem, which is listed as the first safety hazard that our company must solve in the National Safety Month activities

2. Introduction to electrical circuit

the lifting mechanism of the tower crane adopts the speed regulation method of changing the polar number. Motor model yztd2502/4/6/24, rated power 24/22/22/3.5kw, rated current 48/45/44/42a, rated speed 2830/1420/930r/min, connection yy/△/yy/y, working system 25%/40%/40%/25%, insulation grade B. The stator of this motor is equipped with two sets of mutually independent windings. The micro speed gear (24 poles) and low speed gear (6 grades) share a set of windings, and the medium speed gear (4 grades) and high speed gear (2 poles) share a set of windings. Different working pole numbers can be obtained by changing the winding connection. Because of tripping, we don't need to develop new products from scratch. The faults all occur when the micro speed gear and low speed gear work. Now, only the electrical schematic diagram of the micro speed gear and low speed gear is drawn in Figure 1

Figure 1 original design drawing

when the system works normally, lkm3 AC contactor is closed, lkm4 and lkm5 AC contactors are separated, and the motor is in a 24 pole micro speed working state; Or lkm4 and lkm5 AC contactors are closed, lkm3 AC contactor is separated, and the motor is in the low-speed working state of 6 poles. Lkm3, lkm4 and lkm5 must not be closed at the same time, otherwise the line will be closed. 1. The well cover pressure fatigue testing machine adopts the relatively new technology of the 21st century in hardware design. Common fault 4: the technology produces short circuit fault

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